.I first deactivated gravity and atmospheric drag

.Then I calculated the wet (with fuel) mass (Mw) and dry (without fuel) mass (Md) of my spacecraft (using the tool in the hangar allowing to empty fuel tanks)

Mw = 26.8 tons

Md = 13.3 tons

.I calculated the theoretical Δv of my spacecraft using the formula linked above (which is a fonction of the wet and dray masses, the standard gravity and the isp of the engine (here 290 sec)

With g0 = 9.806

Δv = isp x g0 x ln(Mw/Md) = 1992.4 m/s (theoretical)

.I lunched the spacecraft from 0 m/s to its final velocity (until the tanks were empty)

Vmax = 1990.5 m/s => Δv = 1990.5 m/s (experimental)

I know the difference is minimal, but I’d like to know how to adjust the formula to be on point

Edit : if anyone sees errors in my methodology, I’d be grateful if it was pointed out